This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2000-321190 filed on Oct. 20, 2000, and 2001-285386 filed on Sep. 19, 2001.
1. Field of the Invention
The present invention relates to a heat pump cycle capable of switching between cooling and heating, which is suitable for use in a supercritical heat pump cycle in which a refrigerant pressure exceeds the critical pressure of a refrigerant.
2. Description of Related Art
JP-A-2000-130878 discloses a heat pump cycle capable of switching between cooling and heating. In the heat pump cycle, an internal heat exchanger is provided for performing heat exchange between a suction side refrigerant to be sucked into a compressor and a discharge side refrigerant discharged from the compressor. A pressure reducing unit is disposed between an internal heat exchanger and an indoor heat exchanger, so that heat exchange is performed between the suction side refrigerant and the discharge side refrigerant at the time of a cooling operation, and heat exchange is not effected between the suction side refrigerant and the discharge side refrigerant at the time of a heating operation.
In a refrigerating cycle, since lubricating oil is mixed into a refrigerant to lubricate a sliding portion in a compressor, an oil return hole is provided in an accumulator for extracting a liquid phase refrigerant containing lubricating oil. The refrigerant extracted through the oil return hole and containing the lubricating oil is supplied to a suction side of the compressor together with a gas phase refrigerant separated in the accumulator.
The amount of heat equivalent to the work of compression of the compressor is used for heating at the time of a heating operation, so that a circulating mass flow rate of the refrigerant required at the time of the heating operation is generally smaller than a circulating mass flow rate required at the time of a cooling operation.
Thus, when the size of the oil return hole is designed so that an optimum amount of lubricating oil is attained at the time of the cooling operation, the amount of lubricating oil needed at the time of the heating operation may not be attained.
On the contrary, when the size of the oil return hole is designed so that an optimum amount of lubricating oil is attained at the time of the heating operation, the amount of liquid phase refrigerant sucked into the compressor is increased, so that the work of compression of the compressor is increased and a Coefficient Of Performance (COP) of the heat pump cycle is worsened.
An object of the present invention is to prevent of a Coefficient Of Performance (COP) from being worsened while sufficiently attaining a lubricating oil amount needed at the time of a heating operation.
According to the present invention, a compressor sucks and compresses a refrigerant. An outdoor heat exchanger performs a heat exchange between outdoor air and the refrigerant. An indoor heat exchanger performs a heat exchange between indoor air blowing into a vehicle compartment and the refrigerant. An accumulator separates the refrigerant into a gas phase refrigerant and a liquid phase refrigerant containing lubricating oil. The accumulator includes an oil return hole for extracting the liquid phase refrigerant containing lubricating oil, and allows the liquid phase refrigerant containing the lubricating oil extracted from the oil return hole and the separated gas phase refrigerant to flow out to the compressor. An internal heat exchanger performs a heat exchange between a discharge side refrigerant flowing between the indoor heat exchanger and the outdoor heat exchanger and a suction side refrigerant flowing out of the accumulator. A first pressure reducing unit is provided in a refrigerant passage allowing the indoor heat exchanger to communicate with the internal heat exchanger. The first pressure reducing unit decompresses the refrigerant flowing out of the internal heat exchanger at a time of the cooling operation to cool the air blowing into the vehicle compartment. A second pressure reducing unit is provided in a refrigerant passage allowing the outdoor heat exchanger to communicate with the internal heat exchanger. The second pressure reducing unit decompresses the refrigerant flowing out of the internal heat exchanger at a time of the heating operation to heat the air blowing into the vehicle compartment.
By this, also at the time of the heating operation, the liquid phase refrigerant is vaporized by heating the liquid phase refrigerant containing lubricating oil in the suction side refrigerant by the discharge side refrigerant, so that the amount of the liquid phase refrigerant sucked into the compressor is decreased.
Accordingly, the work of compression of the compressor is prevented from increasing, and an opening area of the oil return hole can be expanded to such a degree that an optimum amount of lubricating oil is attained at the time of the heating operation.
Further, since the enthalpy of the discharge side refrigerant is lowered by performing a heat exchange between the discharge side refrigerant and the suction side refrigerant, the amount of heat absorption in the indoor heat exchanger at the time of the cooling operation, and the amount of heat released in the indoor exchanger at the time of the heating operation are increased.
As described above, according to the present invention, the amount of lubricating oil needed at the time of the heating operation is attained, and the COP of the heat pump cycle is prevented from being worsened.